The present invention relates to the manufacturing of grinding wheels.
According to a known manufacturing method a mixture of abrasive grains, a particulate binder material and if desired some fillers are poured into an open mold, then the mold content is leveled and submitted to pressing.
The filling and leveling of the mold can be carried out outside the press, then the filled up mold may be placed in the press for compaction. This sequence of processing steps takes a relatively long time so that the manufacturing rate is relatively slow.
In following another known procedure, filling and leveling of the mold may be performed directly inside the press, but in this case it is necessary to provide enough space between the upper part of the mold and the die of the press to accommodate the leveling equipment, which consequently increases length of the die stroke and slows down operations.
It is also known to manufacture cast resin cores in molds by blowing a raw batch into the empty mold. According to this method a load including sand together with a resin binder is introduced into a hopper or a container which communicates through a passage with a cavity, whose shape corresponds to that of the core to be produced. Afterwards a relatively high pressure is suddenly applied to the container, with the result that the sand and binder mixture is blown out of the hopper and through the above-mentioned passage into said cavity.
Attempts have been made in the past to manufacture grinding wheels in this manner. However difficulties were encountered which resulted from the fact that it was impossible to obtain the necessary homogeneity and strength properties required for a grinding wheel as compared to a casting or core made of resin alone.
One particular difficulty encountered in attempts to blow mold grinding wheels resulted from the fact that the conventional mixture for manufacturing a grinding wheel consists of abrasive particles whose grain size is determined by the wheel specification and a resin binder in the form of much finer particles, so that the difference in grain sizes between both components permitted some segregation by sizes during filling of the hopper or container with this mixture and further segregation of the different grain sizes occurred when the latter is expelled by means of pressure, air or gas which segregation destroys the homogeneity of the mix rendering it useless for the manufacture of grinding wheels.